Which language learning company first introduced 'adaptive packaging' that changes language difficulty based on learner progress?

Test your knowledge about innovative packaging design in the language learning industry! The way language learning products are packaged can significantly impact consumer perception and engagement. This trivia question focuses on a revolutionary packaging design that changed how consumers interact with language learning materials. Even packaging design can influence language acquisition!

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Rosetta Stone with their Neural Response Packaging (2017)
Duolingo with their Progressive Difficulty Boxes (2019)
Babbel with their Linguistic Advancement Containers (2018)
Pimsleur with their Cognitive Adaptation Packaging (2020)